Class-ceramic materials comprise crystalline phases and glassy phases. Due to the unique structures, they have exceptional physical properties, such as strength and coefficient of thermal expansion that enable them to be used in a wide range of products. A particularly interesting application of β-quartz and/or β-spodumene glass-ceramic material is in cooktop plates, fireplace windows and the like. A series of glass-ceramic cooktop plates and fireplace windows have been commercialized successfully.
The fabrication process of glass-ceramic material typically includes three steps: (i) melting of the precursor glass; (ii) forming the precursor glass into desired shapes; and (iii) heat-treating the shaped glass object to such that crystalline phases are formed in the glass article. The last step typically comprises two steps: (iii-a) treating the glass article at a relatively lower temperature where crystalline nuclei are allowed to form, which is typically termed the step of nucleating; and (iii-b) treating the glass article with nuclei at a higher temperature where the crystalline phase is allowed to grow to a desired extent.
As is typical in glass melting, in step (i), a fining agent is employed in making the precursor glass. Such fining agent releases gas at elevated temperature where the glass is melted and fined. The released gas facilitates the escaping of the gas bubbles which would otherwise be trapped inside the glass. Historically, As2O3 and/or Sb2O3 were used as effective fining agents. Due to increasing environmental concerns, As2O3 and Sb2O3 are to be phased out from such products in the near future. Therefore, there is the need of developing an alternative fining system that can effectively fine the glass during the glass melting step without significantly negatively impacting the forming step and the desired properties of the intended glass-ceramic articles and the fabrication process.
The present invention satisfies this need.